The installation of a cable into a preformed bore is particularly useful in the art of mine roof supports for reinforcing an unstable rock formation above a mine roof. Once the bore is drilled through the unstable rock formation and through a stable rock formation behind the unstable one, the cable is inserted into the bore with a retainer adapted for locking the free end of the cable at the bottom of the bore. Concrete is then injected into the bore and a retaining nut connected to the cable is installed at the outer edge of the bore for retaining adjacent rocks.
The retainer is generally an expansion shell gripping the stable rock formation surrounding the bottom of the bore. For some applications, more particularly for temporary roof supports, the retainer can be a bend in the free end of the cable. Temporary roof supports are often used for the safety of the workers who are drilling holes for the installation of blasting charges.
One of the problems with the installation of such cables is that they have to be cut somehow since they are usually commercially purchased in rolls where the cable has a great length. The long cable is generally cut with a circular saw blade or with a cutting torch for providing smaller cables of suitable length. It is generally very dangerous to cut the cable with saw blades or cutting torches in a mine draft because of the risks of explosions due to the presence of flammable gases which may be accidently lighted by the sparks generated when cutting the cable with a saw blade or by open flame of the cutting torch. The usual way of resolving that problem is to cut the cable outside the mine and provide precut cables of predetermined length on site. However, due to the unstable conditions of the rock strata above the mine roof, it is sometimes necessary to drill a bore hole to a greater depth than what is usually done, thereby creating the need of carrying precut cables of various lengths on site.